In the beginning, there was the World Wide Web. Compared with
desktop applications, web applications were slow and clunky. People liked web applications anyway because they were
conveniently available from anywhere, on any computer that had a browser. Then Microsoft created XMLHttpRequest
in Internet Explorer 5, which let
browser-side JavaScript communicate with the web server in the background without
requiring the browser to display a new web page. That made it possible to develop more fluid and responsive web applications.
Mozilla soon implemented XMLHttpRequest in its browsers, as did Apple (in the Safari browser) and Opera.

XMLHttpRequest must have been one of the Web's best kept
secrets. Since its debut in 1998, few sites have used it at all, and most developers, if they even knew about it, never used it.
Google started to change that when it released a series of high-profile web applications with sleek new UIs powered by XMLHttpRequest. The most visually impressive of these is Google Maps, which gives you
the illusion of being able to drag around an infinitely sizable map in its
little map window.

While Google's prominent use of XMLHttpRequest dramatically
demonstrated that vastly improved UIs for web apps were possible, it was Jesse James Garrett's February
18 essay that finally gave this technique a usable name: Ajax (Asynchronous JavaScript and XML). That was the tipping point. Without knowing
it, we as an industry had been waiting for this, and the new Ajax name spread like wildfire. I have never seen such rapid and near universal adoption of a new technology moniker!